How old can chicks be to give to a broody hen?

The feed store got their last batch of chicks today and I picked up two for my broody BR hen. Chicks are in the brooder tonight so I can see that they are eating/drinking/pooping. I planned to stow them under mama tomorrow evening and then keep a close eye on the new family. But I need to be away tomorrow night and don't want my husband to have to deal with it.

So, my question:
can the chicks stay in the brooder one more night and then I can give them to mama on Sunday evening? Or should I give them to mama tomorrow (Sat) night and cancel my trip?

This is the first time I'll try to use a hen to raise chicks so we're both newbies. She's from the first batch of five chicks that we got four years ago and this is the first time she's been broody. My concern is mostly whether she will more readily accept the chicks the younger they are; will a day or two make a difference?

The yonger the better... she may accept them but the problem is that THEY might get used to being alone and be afraid of chickens (creatures they're not used to)... so you can just toss them under her during the day and give it a chance... if she accepts them a relief.... if not... give it a shot at night...

I gave her the chicks this morning and -- for a few minutes -- I was elated. I tucked one chick under each wing, the chicks quieted immediately and she settled and gave some soft clucks.

A few minutes later she started to get restless and began pecking low at her wings, where the chicks were. I watched a bit longer but the pecks seemed to get stronger so I removed the chicks and let them peep in the next nest box, to see if she might go to them. She didn't. I held a chick and moved it toward her, enclosed in my hand so that if she pecked she would get me and not the chick. She pecked. Not certain, but it seemed to me that she was pecking at the peeping chick, rather than the hand that was holding it hostage.

Overall, she seemed frozen and staring, didn't really move much and never took her eyes off my hand with the chicks. I removed them -- they're back in the brooder, she's still in the nest box.

Ok you should of just toss the under her body.. she shouldn't see them immediately.... she should think that they hatched under her not visitors... just let them settle their for an hour or so then she'll know that her eggs (that are not their) hatched and she will accept them (maybe)... for the pecking thing... you should haven't hold it a let it peep in your hand... she will theck anything that moves in the hand... she won't differentiate between the hand and the chicks just peck the think that moves more (the chick) in a try to defend the chick that is peeping... that happened lots of times with me... but when I put it back she will let him cuddle under her... so give it a try tonight again.... and leave him till morning... .she won't see them ir move much at night and they will sleep and won't stress herout..